The present invention relates to an apparatus for recording and reproducing informations on an information recording medium, such as an optical disc.
When information is recorded and reproduced on a recording medium such as an optical disc with a laser beam, if the recording surface of the optical disc and a light beam incident angle are changed due to a warp and a surface deflection of the optical disc, the distribution of light beam diameter and intensity becomes changed largely as shown in FIG. 1. If, in the case of information recording, the light beam power is decreased on the recording surface of the optical disc, the length of a pit to be recorded becomes changed.
Provided that the writable beam power is PW, the length of pit is illustrated as shown in FIG. 1(a) when the recording surface of the disc is not slanted, is illustrated as shown in FIG. 1(b) when the recording surface is slanted in the (+) direction, and is illustrated as shown in FIG. 1(c) when the recording surface is slanted in the (-) direction.
As described above, if the write beam intensity on the recording surface of the optical disc is changed due to the warp and the surface deflection of the disc, the writing conditions on the recording surface of the optical disc become unstable.